Thyrotropin releasing factor (TRF) and melanocyte-stimulating hormone release-inhibiting factor (MIF) degrading enzymes will be isolated from human plasma by affinity chromatography. Inhibitors of these proteolytic enzymes will also be synthesized; these inhibitors may be useful as new drugs. An attempt to isolate the TRF receptor from membrane preparations of cultured pituitary cells will be made by covalently attaching a radioactive derivative of TRF to the TRF receptor molecule.